After capturing Troy, Telamon marries Hesione, Laomedon’s daughter. Peleus is already married to the goddess Thetis. Jupiter, Peleus’s grandfather, had lusted after Thetis, but didn’t want to sleep with her for fear that she would give birth to a child who would become more powerful than himself. Instead, Jupiter tells Peleus to have a child with Thetis. One day, Peleus finds Thetis lying naked and asleep in her underwater cave. When he wakes her and tries to woo her, she resists him, so he grabs her and tries to rape her. She escapes by changing shape, first into a bird, then a tree, and finally a ferocious tiger.
Because Thetis is a goddess, Jupiter worried that the child he would have with her would have the power to overthrow him. This might explain part of the reason why Jupiter likes to sleep with mortal women and have children with them. In so doing, he maintains his position as the head of all the gods and does not allow the world to produce anything that could be stronger than him. This shows that even the gods aren’t above self-interest. This story is also an example of metamorphosis saving someone, as Thetis’s transformations help her escape Peleus’s attempted assault.
Peleus flees Thetis’s cave and decides to ask the sea-gods for advice. One of them tells him to sneak up on Thetis while she sleeps and ensnare her in a rope, preventing her from changing shape. Peleus follows the sea god’s advice. When Thetis wakes up and tries to change shape, she is too tightly bound. She gives in to Peleus, deciding that the gods are helping him, and soon gives birth to Achilles.
After Peleus has overpowered her abilities, Thetis then realizes that the gods are on Peleus’s side. The gods, in this case, are another thing—besides Peleus’s force—that manipulates Thetis into having sex with Peleus. In this way, the gods can be seen as a cruel rather than a protective presence.